The inventors have heretofore proposed a process for obtaining an ink jet head which comprises anodically connecting borosilicate glass to a silicon substrate having fine grooves formed thereon to form various ink passages thereon as disclosed in JP-A-6-23980 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-6-31914. This process enables an easy production of a large amount of ink jet heads at a low-cost.
On the other hand, an aqueous ink for ink jet recording described in JP-A-2-255774 comprises water, a water-soluble dye, a drying inhibitor and a penetrant. As the penetrant there may be used one comprising a compound represented by the following general formula: ##STR1##
wherein R.sub.1 represents a hydrogen atom, a methyl group, a methoxy group, a chlorine atom or a bromine atom; and m represents an integer of from 1 to 5 (hereinafter referred to as "compound (1)") and an ethylene oxide adduct of butyl alcohol wherein the number of moles of added ethylene oxide is from 1 to 5 (hereinafter referred to as "compound (2)"), and optionally a propylene oxide adduct of butyl alcohol wherein the number of moles of added propylene oxide is from 1 to 5 as a penetrant (hereinafter referred to as "compound (3)"), whereby the surface tension thereof is from 30 to 40 dyn. In this arrangement, the evaporation of water or the like from the ink through the nozzle of the recording head can be suppressed, inhibiting the rise of the viscosity of the ink and hence enabling normal ink jetting. Further, a highly stable ink jetting can be effected, enabling a good quality printing.
However, when a recording head made of borosilicate glass as described in JP-A-6-23980 and JP-A-6-31914 filled with a water-soluble ink for ink jet recording as described in JP-A-2-255774 is allowed to stand at high temperatures over an extended period of time, borosilicate glass in contact with the water-soluble ink elutes with the ink. When the water in the ink evaporates from the surface of the nozzle, the solution of borosilicate glass is supersaturated, causing borosilicate glass to be deposited on the surface of the nozzle. This causes the recording head to be clogged, disabling the jetting of ink droplets and hence causing a phenomenon of omission of recorded image, i.e., so-called dot failure. Further, if ink droplets are jetted leaving deposits of borosilicate glass in the nozzle, the ink shots can be malpositioned (a phenomenon in which an ink droplet cannot fly perpendicular to the recording medium), deteriorating the printing quality.
In order to solve these problems, a recording head molded from a plastic or metal may be used. With this arrangement, the substances constituting the ink passage don't elute and deposit. Thus, the evaporation of ink components such as water from the nozzle of the recording head can be suppressed, inhibiting the rise of the viscosity of the ink and hence enabling normal ink jetting. Further, stable jetting can be conducted, enabling a good quality printing.
However, the recording head molded from a plastic or metal requires a much production cost to reduce the nozzle diameter to a good precision. Thus, the resulting ink jet printer is very expensive. However, if the ink jet printer is used with the nozzle diameter left large, the ink discharge rate per dot is increased, making it extremely difficult to print at a high resolution and hence making it impossible to provide a high fineness and a high printing quality in printing.
As another method for inhibiting the deposition of borosilicate glass there may be used a method which comprises frequently restoring the nozzle (externally pressing and sucking off the ink from the nozzle to keep the viscosity of the ink constant). However, this method is disadvantageous in that a large amount of the ink must be consumed for the restoration of the nozzle. The method is also disadvantageous in that the wasteful consumption of the ink forces the user to frequently renew the ink jet cartridge. After all, this method presents an inconvenience to the user.